China and India have accounted for more than half of the total number of global deaths attributable to air pollution in 2015, a study published on Tuesday said.

Research by the US-based Health Effects Institute (HEI) showed that air pollution caused more than 4.2 million early deaths worldwide in 2015, making it the fifth highest cause of death, with around 2.2 million deaths in China and India alone.

The institute, which has also launched an online database showing the global impact of pollution on health, said 92 per cent of the world's population lives in areas with unhealthy air.